A current model scanning electron microscope is requested for use in a central campus multi-user facility. The SEM currently in use is the only one available in the area, it is 12 years old, and it is an orphan; new parts are no longer available for repairs. This has become a severe problem: the performance of the current instrument is declining and it is frequently out of service while we wait for used parts or to have them custom built. The need for an efficient multi-user instrument is particularly urgent due to a substantial increase in the number of labs at our institution that use or need to use a modern SEM. The requested JEOL JSM-5800LV has a number of features that will make it deal for our large user group. The build in computer can store 160 different sets of column operating conditions. This will allow long-term storage and retrieval of sets of optimal alignments for different standard accelerating voltages and also of unique, user-specified specimen illumination conditions. The computer can also store and automatically return to 160 different sample viewing positions using a fully automated return to 160 different sample viewing positions using a fully automated motorized. In addition, the automated zoom condenser allows rapid high to low resolution selectability without any refocusing or adjustments. These features will allow inexperienced users to work efficiently with the instrument. A further increase in efficiency will be provided by an airlock chamber system that allows specimen exchange without altering the chamber vacuum. It will increased the effective operating time of the instrument, particularly for high resolution work, by eliminating the wait for vacuum restabilization ever time a new specimen. The low vacuum capability of the new instrument will also allow important new approaching: 1) low accelerating voltage imaging of uncoated specimens: frozen, fixed, or untreated, and 2) high accelerating voltage elemental analysis with an EDS system. The user- friendliness and the low-vacuum capability will make the requested instrument heavily used and invaluable to our large group. Access will be convenient, as it will be house in a mew microscopy facility that is under construction for the Indiana Molecular Biology Institute. This central facility will be staffed with a full time supervisor and will be available for meritorious research use University-wide. The current user group consists of fifteen research labs from six different departments. The NIH- funded projects that will use the new SEM include studies of: 1) subcellular motility in Drosophila, 2) Caulobacter differentiation, 3) human erythrocyte membrane structure. 4) auxin action in Arabidopsis, 5) Delta-based cell-cell interactions in Drosophila, 6) microtubule isoform function in Drosophila, 7) the evolution of development. 8) radiation repair and meiosis in Coprinus, and 9) the effects of tamoxifen on the uterine endometrium.